Refrigerating system including hot gas defrosting circuit



REFRIGERATING SYSTEM INCLUDING HOT GAS DEFROSTING CIRCUIT Filed Dec. 20,1957 INVENTOR. FRANK A. SCHUMACHER HIS ATTORNEY United States Patent iceREFRIGERATING SYSTEM INCLUDING HOT GAS DEFROSTING CIRCUIT Frank A.Schumacher, Louisville, Ky., assign'or to General Electric Company, acorporation of New York Application December 20, 1957, Serial No.704,184 5 Claims. (Cl. 62-278) The present invention relates torefrigerating apparatus and is more particularly concerned with arefrigerating system including an improved circuit arrangement foremploying compressed refrigerant gas-to warm the evaporator component ofthe system to defrosting temperatures.

In the copending application of Clyde J. Nonomaque, Serial No. 698,462,filed November 25, 1957, and assigned to the same assignee as thepresent invention, there is described and claimed a refrigerating systemincluding an auxiliary hot gas defrosting circuit for quickly andeffectively employing hot compressed refrigerant to defrosting theevaporator component of the refrigerating system. It is to be understoodthat the present invention is an improvement over the invention of theNonomaque application and I therefore do not herein claim as myinvention anything shown or described in said Nonomaque application,which is to be regarded as prior art with'respect to the presentapplication. 1

The refrigerating system described and claimed in the Nonomaqueapplication comprises a compressor, a condenser, a fixed flow restrictorand an evaporator connected to form a normal refrigerating circuit. Forthe purpose of periodically raising the evaporator to defrostingtemperatures by means of hot compressed refrigerant from the compressor,there is provided an auxiliary circuit connected between the high andlow pressure sides of the normal refrigerating circuit and in parallelwith at least that part of the normal circuit including the fixed flowrestrictor and the evaporator. The auxiliary circuit includes a defrostportion in heat exchange with the evaporator and a flow restrictingmeans between the defrost portionand the compressor so that upon openingof a normally closed valve in the auxiliary circuit, hot compressedrefrigerant will flow through the defrost portion ofthe auxiliarycircuit in heating relation with the evaporator where condensation ofrefrigerant in the defrosting portion quickly and effectively warms theevaporator to defrosting temperatures.

In the refrigerating system described and claimed in the aforementionedNonomaque application, the lesser flow resistance of the flowrestricting means in the auxiliar'y circuit as compared with the flowresistance of the fixed flow restrictor in the refrigerator circuitunder existing conditions is relied upon to cause substantially all ofthecompressed refrigerant to flow through the defrost circuit during thedefrosting operation even though both circuits are in communication withthe compressor. While these desired flow conditions are obtained undermost operating conditions, it has been found that under low ambientconditions the condenser temperature may be'so low as to cause somecondensation of refrigerant in the'. condenser even during the earlystages of defrost operation of the system with the result that condensedrefrigerant from the condenser willfiow through the fixed flowrestrictor and into the evaporator. The resultant cooling'efiect on theevaporator partially olfsets' 2,907,184 Patented Oct. 6, 1959 theheating effect of the defrost circuit and thereby slows down the rate oftemperature rise of the evaporator and hence increases the timenecessary to remove the accumulated frost from evaporator. It istherefore a primary object of the present invention to provide means forsubstantially reducing this low ambient fiow of. refrigerant through therefrigerating circuit during defrost operation of the above-describedsystem.

In accordance with the present invention, condensed refrigerant isreduced in flow from the condenser to the evaporator by placing aportion of the auxiliary circuit between the control valve and thedefrost portion of the Nonomaque system in heat exchange relationshipwith the refrigerating circuit ahead of or in contact with the capillaryflow restrictor.

More specifically, the refrigerating system of the present inventioncomprises an evaporator, a compressor, a condenser and a capillary flowrestrictor, and conduit means connecting the compressor, condenser,capillary flow restrictor and evaporator in closed series-flowrefrigerating circuit whereby the compressor normally withdraws lowpressure refrigerant from the evaporator and discharges high pressurerefrigerant to the condenser. For periodically raising the evaporator todefrosting temperatures by means of hot compressed refrigerant from thecompressor, there is provided an auxiliary circuit having its inletconnected to the refrigerating circuit between the compressor and thecapillary flow restrictor and its outlet end connected to the lowpressure portion of the refrigerating circuit between the evaporator andthe compressor. This auxiliary circuit includes in series connection, anormally-closed fiow control valve adjacent theinlet to the auxiliarycircuit, a defrost portion 1 in heat exchange relationship with theevaporator and a normal refrigerating circuit during defrost operationof the system, a portion of the auxiliary circuit carrying hotcompressed refrigerant is disposed in heat exchange relation with aportion of the normal circuit between the condenser and the outlet endof capillary flow restrictor. This heat interchange causesrevaporization of the condensed liquid so that the flow of refrigerantthrough the capillary flow restrictor is reduced causing anyrefrigerating effect in the normal circuit to be negligible duringdefrost operation. 1

For a better understanding of the present invention reference may be hadto the accompanying drawing in which the single figure is a diagrammaticillustration of a refrigerating system embodying the hot gas defrostarrangement of the present invention. 4

With reference to Fig. 1 of the drawing, the system comprises the usualcomponents including a compressor unit 1, a condenser 2, a capillaryflow restrictor 3, a cooling or evaporator unit comprising a serpentineevaporator circuit 5 and an accumulator 6, and a suction line 7connected in closed series-flow relationship. f i

The motor compressor unit 1 comprises a motor 13 for driving acompressor 14, the two being sealed in a hernormal refrigerating systemand is therefore filled with .low pressure refrigerant in coolingcontact with the motor 13, while the compressor 14 having its inlet 14acommunicating withthe .case 15 withdraws gaseous refrigerant from thecase and discharges high pressure refrigerant directly to the dischargeline 17 connected to the condenser 2. In this system, the evaporatorunit and the case 15 form the low pressure side of the normalrefrigerating-circuit while the compressor and condenser comprise thehigh pressure side. The evaporator circuitS andin the illustratedmodification, also the accumulator 6, form part of .a roll-bondevaporator'structure 8 which includes the plate or body 9; theaccumulator 8 in'such case conveniently being composed of a plurality ofintersecting vertical and horizontal tubular portions in accordance withthe known practices.

Also in accordance with the usual practice, the suction line 7 isin-heat exchange relationship with -a portion of the capillary tuberestrictor 3 as indicated at 1-1 whereby condensed refrigerant passingto the evaporator is further cooled by the refrigerant vgas flowingthrough'the suction line to the compressor.

To accomplish the defrosting of the evaporator structure'8, there isprovided an auxiliary circuit 18 which is in parallel flow relationshipwith the evaporator and the restrictor portions of the normalrefrigerating circuit and which is designed to form with certainelements of the normal refrigerating circuit a defrost circuit .toconduct compressed refrigerant gas from the high pressure side of thesystem into heat exchange relationship with the evaporator structure 8for the purpose of warming this structure :to defrosting temperatures.auxiliary circuit is connected to the discharge line 17 leading from thecompressor to the condenser 2 and a normally closed valve 20 operated bya solenoid 28 is provided for controlling the flow of refrigerantthrough the auxiliary circuit 18. The auxiliary circuit also includesan-evaporator defrosting portion composed of a first section 21 in heatexchange relationship with the serpentine evaporator and a secondsection 22 in heat exchangerelationship with the accumulator 6.

The outlet end of the auxiliary circuit is connected to the suction line7 as indicated by the numeral '24 by means of a restrictor tube 25having a lower restriction than capillary tube 3 but which providessuflicient restriction to flow refrigerant through the auxiliary circuitto maintain the refrigerant gas in the defrosting sections 21.and 22 atcondensing pressures.

In the normal operation of the refrigerating system, the motorcompressor unit 1 withdraws vaporizedrefrigerant from the top of theaccumulator 6 through the suction line 7 and discharges compressedrefrigerant to the con denser 2. The refrigerant liquified in thecondenser 2 passes through the capillary flow restrictor .3 into theevaporator circuit 5 where, at a lower pressure, it isvap'orized by theabsorption of heat from a refrigerator cabinet (not shown) to cool thecontents of the cabinet. .Any liquid refrigerant not evaporated in theevaporator circuit 5 collects in the accumulator 6; the connection ofthe evaporator 5 to the accumulator preferably being at the lower partof the accumulator while the suction line 7 is connected to the upperportion thereof so that, during normal refrigerating operation of thissystem,zonly gaseous refrigerant is withdrawn from the accumulatorthrough the suction line 7 by the motor compressor unitl.

As a layer of frost collects on the evaporator structure 8 during normaloperation of the refrigerating system, it becomes necessary periodicallyto remove this frost layer in order tomaintain the operating efiiciencyof theevaporator unit. When defrosting of the evaporator structure isdesired, the valve 20 is-opened with result that due to the lower flowrestriction of the auxiliary circuit, substantiallyall of therefrigerantwithdrawn from the accumulator '6'by the compressor then flows from thecompressor into the auxiliary circuit 18 instead of the normalrefrigerating circuit.- In other words When the valve 20 is openedsubstantially all of the refrigerant passes through what may be 'termeda'defrost circuit comprising, in

The inlet .end 19 of the series=flow connection, the compressor 14,thedefrost sections 21 and 22, the restrictor 25 and the case 15. In thedefrost sections 21 and 22, which correspond to the condenser componentof a inormal refrigerating circuit, the hot compressed refrigerantcondenses liberating heat which melts the frost accumulated on theevaporator structure 8. The condensed refrigerant then flows throughrestrictor 25 andireturns to the compressor case 15 as a liquid or'asa-mixtureof;liquidlandigas.

By means of the auxiliary circuit 18 including the defrost sections inheat exchange relationship with the evaporator and accumulator, both the'stored'dieat in the compressor case and the inputwatts to thecompressor motor .are used .as heat ISOUECQS 'for defrosting ztheevaporator structure. Since the stored compressor heat is quicklydissip-ated,the principal source of heat energy is the input watts tothe motor during the remaining portion of the defrost period, thisenergy being transferred by the refrigerant to the evaporator structureas heat energy. To increase the input watts to the "compressor "motor inorder to providequick defrosting of the evaporator, the entire systemis'preferably designed that the load on'the compressor motor'ishighduring the'defrostcycle. This result is attained by designing 'thesystemfor higherpressure operation during the defrost cycle with themajor partofthe increased load on the motor'being obtained by an increase in thelow "side or suction pressure resulting from a concentration ofmost ofthe'refrigerant charge in 'the compressor case 15 or more broadly in thelow side portion of the circuit'b'etweenthe restrictor 25 and thecompressor 14 during'defrost operation ofthe system. As this refrigerantcools the compressor-motor 13, all of the heat liberated'by'the motor istransferred to the circulating refrigerant and therefore to the 'de'frostingiportions of the auxiliary circuit '18 in heat exchangerelationship with'the evaporatorstructureS. To obtain an increasedamount of heat fromthe compressor during defrost operation, the-mainrefrigeratingcircuit'is preferably designed so that as the accumulator*6 is warmed duringthe defrost'op'eration, the liquidrefrigerant storedtherein is partially vaporized and rtransferred through the suction line7 to the compressor case as a mixture of liquid and gas where itserves'to 'raisethe low side'pressure on the compressor 14.

The refrigerating system as thus far described with reference'to thedrawing is more'specifically described in'the aforementionedfNonomaque'application. Byfollowing the teachingsof that application,restrictors'S and 25 are so proportioned as to cause substantially allof the refrigerant'to flow through the auxiliary circuit when the valve20 is open even though both the auxiliary circuit "18 and the normalrefrigerating circuit including the condenser 2, the restrictor 3 andthe evaporator 5 are in .open connection with the compressor. The'lowerresistance'to refrigerant flowprovided'by the auxiliary circuit 18causes most .of the refrigerant 'to how through this circuitparticularly under high ambient conditions where the condenser which isat ambient temperature will be filled only with gaseous rather 'thanliquid refrigerant during'the defrost cycle. I

However, it has been found that while quick and efficient defrosting ofthe evaporator circuit is obtained in accordancewith theNonomaque'invention under normal orhigh ambient temperature conditions,under relatively low ambient conditions of, for example, 'from 40 to'60" F., the time required for defrost maybe disproportionately long. Ithas been found that this prolonging .of the defrost period at lowambients was caused'by refrigerant condensing in the condenser atlowarcibients and flowing to the evaporator as a'liquid Where it producedrefrigeration opposing the-defrosting action of the warm refrigerant inthe auxiliary circuit. refrigerating effect was noted particularlyduring-the later stages of defrost operation during which the systempressures are highe and ther ss r'e in the condenser reaches refrigerantliquificationpoint'. "This liquifred condition permits approximately 6times the mass flow rate of the gaseous state; I

In accordance with the present invention, the flow of refrigerantcondensed in the condenser during the defrost period is reduced by heatinterchanging a section of the auxiliary circuit 18 with a portion ofthe normal refrigerating circuit ahead of or in contact with thecapillary tube 3. Preferably this heat exchanger is between the outletfrom the condenser and the first part of the capillary tube 3 asindicated at 29 so that the heat of the hot compressed refrigerant fromthe compressor passing through the auxiliary circuit 18 will maintainthis portion of the normal refrigerating circuit attemperatures whichwill vaporize any condensed refrigerant leaving the condenser 2 therebysubstantially increasing the flow restriction of the capillary 3 which,as is well known, will conduct gaseous refrigerant at a much slower ratethan liquid refrigerant. v

Tests have indicated that by providing the heat interchange 29 betweenthe auxiliary circuit 18 and the normal refrigerating circuit, completedefrost of the evaporator structure 8 could be obtained as quickly atlow ambient said condenser and the outlet end of said capillary flowrestrictor to maintain said section at refrigerant vaporizingtemperature and thereby limit flow of refrigerant to said evaporatorduring operation of said system with said valve in the open position. i

2. A defrostable refrigerating system comprising an evaporator unit, acompressor, a condenser, and a capillary flow restrictor, conduit meansconnecting thecompressor, condenser, capillary flow restrictorandevapora tor unit in closed series-flow refrigerating circuit wherebysaid compressor normally withdraws low pressure refrig erant from saidevaporator and discharges high pressure refrigerant to said condenser,and means for periodically raising said evaporator to defrostingtemperature by means of hot compressed refrigerant from said compressorcomprising an auxiliary circuit including alnor mally closed valve forcontrolling flow of refrigerant to said auxiliary circuit, said circuithaving its inlet co'n nected to said refrigerating circuit between saidcomtemperature conditions of for example 40 F. as under the high ambienttemperature conditions of 80 to 100 F. In other words it has been foundthat at low ambients the time required for complete defrosting of theevaporator structure employing the heat interchange 29 is about halfthat'required if no heat interchange between the auxiliary circuit andthe normal refrigerating circuit is provided ahead of the restrictor'3.

The refrigerating system of the present invention is adapted of courseto be controlled either manually or automatically. A suitable electricalcircuit for automatic control is described in the copending Nonomaqueapplication. It will also be understood that the' present invention isnot restricted to the particular system illustrated in the accompanyingdrawing but is equally applicable to various modifications orarrangements of the auxiliary circuits and normal refrigerating circuitssuch as are shown for example in the aforementioned Nonomaqueapplication. Therefore, While there has been shown and described aspecific embodiment of the invention, the invention is not limited tothe particular construction shown and described and it is intended bythe appended claims to cover all modifications within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A defrostable refrigerating system comprising an evaporator unit, acompressor, a condenser, and a capillary flow restrictor, conduit meansconnecting the compressor, condenser, capillary flow restrictor andevaporator unit in closed series-flow refrigerating circuit whereby saidcompressor normally withdraws low pressure refrigerant from saidevaporator and discharges high pressure refrigerant to said condenser,and means for periodically raising said evaporator to defrostingtemperature by means of hot compressed refrigerant from said compressorcomprising an auxiliary circuit including a normally closed valve forcontrolling flow of refrigerant to said auxiliary circuit, said circuithaving its inlet connected to said refrigerating circuit between saidcompressor and said capillary flow restrictor and its outlet connectedto the low pressure portion of said refrigerating circuit between theoutlet end of said evaporator and said compressor, said auxiliarycircuit including, in series connection, a defrost portion in heatexchange relation with said evaporator and a flow restricting means forrestricting the flow of refrigerant from said defrost portion to saidcompressor thereby to maintain refrigerant in said defrost portion atcondensing pressure conditions when said valve is open, a portion ofsaid auxiliary circuit between said inlet and said defrost portion beingin heat exchange relation with a section of said refrigerating circuitbetween pressor and said capillary flow restrictor and its outletconnected to the low pressure portion of said refrigerating circuitbetween the outlet end of said evaporator and said compressor, saidauxiliary circuit including,,in series con nection, a defrost portion inheat exchange relation with said evaporator and a flow'restricting meansfor restricting the flow of refrigerant from said defrost portion tosaid compressor thereby to maintain refrigerant in said defrost portionat condensing pressure conditions when said valve is open, a portion ofsaid auxiliary circuit between said inlet and said defrost portion beingin heat exchangerelation with a section of said refrigerating circuitbetween said condenser and said capillary flow restrictor to main-' tainsaid section at refrigerant vaporizing temperatures and thereby limitflow' of refrigerant to said evaporator during operation of said systemwith said valve in the open, position. I a

3. A refrigerating system comprising a hermetic cornpressor unitincluding a casing and a compressor and a motor for driving saidcompressor Within said casing, a condenser, a fixed'fiow restrictor andan evaporator, conduit means connecting said compressor, condenser,fixed flow restrictor, evaporator and casing to form aclosed series-flownormal refrigerating circuit in which'said compressor withdraws lowpressurev refrigerant frornf said evaporator and through said casing anddischarges high pressure refrigerant to said condenser, said motor'beingcooled by the low pressure refrigerant-in said casing, means forperiodically warming said evaporator todefrosting temperaturescomprising an auxiliary circuit having an inlet end connected to saidnormal refrigerating circuit between said compressor and said fixed flowrestrictor and its outlet end connected to said normal refrigeratingcircuit between the outlet end of said evaporator and said compressor,said auxiliary circuit including a defrost portion in heat exchangerelation with said evaporator and a flow restricting means, conduitmeans connecting said compressor, said defrost portion, said flowrestricting means and said casing to form a seriesfiow defrostingcircuit, a normally closed valve in said auxiliary circuit forpreventing flow of refrigerant through said circuit, opening of saidvalve permitting flow through either said refrigerating circuit or saidauxiliary circuit, said flow restricting means in said auxiliary circuithaving a flow restriction sufiicient to maintain condensing pressures insaid defrost section when refrigerant is flowing through said defrostsection but being substantially less than the flow restriction providedby said fixed flow restrictor when said valve is opened whereby openingof said valve causes substantially all of the circulating refrigerant toflow through said defrost circuit, a section of said auxiliary circuitbetween said valve and said defrost portion being in heat exchangerelation with said refrigerating circuit between said condenser and saidcapillary flow restrictor to vaporize any refrigerant flowing from saidcondenser to said capillary flow restrictor in said normal refrigeratingcircuit and thereby limit flow to reh'igerant to s'ai'd evaporatorduring operation of said system when said valve is in the open position.

t. Arf-rig'eratingsystem comprising a "hermeticcornpressorunitincluding'acasingand a compressor and a motor for drivingsaid compressor within 'said casing, acondensena capillaryfi'ow'restrictor'and an evaporator, conduit means "connecting saidcompressor, condenser, capillaryftow restrictor, evaporator, and'casingto form a closed series-flow norma'l refrigerating circuit in which saideompressorwithdraws low pressure refrigerant from said evaporator andthrough said casing and discharges high .pressure refrigerant to saidcondenser, said motor being cooled by the low pressure refrigerantflowing through saide'asing, means for periodically warming saidevaporator to defro'sti'ngtemperatures comprising an auxiliarycircuithaving an inlet end connected to said normal refrigeratingcircuit'hetweenthe outlet end of said evaporator and 'said'compre'ssor,said auxiliary circuit includinga defrost'portionin heatexchangerelation with said evaporator and a flow restricting means, conduitmeans connecting said compressor, said defrost portion, said flowrestricting means and said casing to form a seriesflow defrosting'circuit, a normally closed valve in said auxiliary circuit forpreventing flow of refrigerant through said circuit, the "flowrestriction provided by saidfiow restricting means in said auxiliarycircuit being sufficie'ntto maintain condensing pressures in saiddefrost section when refrigerant is flowing through said defrostsection, opening of said valve permitting new of refrig'e'rant't'h-roughbo'th said refrigerating circuit and said defrost circuit, aportion of said auxiliary circuit between saidinlet and said defrostportion being in heating relationshi with a portion of saidrefrigerating circuit adjacent the inlet end of said capillary flowrestrictor to vaporize any refrigerant flowing from said condenser tosaid capillary flow restrictor and thereby limit the flow of-refrigerant through said refrigerating circuit when saidvalve is open.

5. A refrigerating system comprising a hermetic compressor unitincluding a casing and a compressor and a motor for driving saidcompressor within said casing, a condenser, a capillary iiow restrictor,an evaporator and an accumulator, conduit means connecting saidcompressor, condenser capillary flow restrictor, evaporator, accumulatorand casing to form a closed series-flow nor- 'n'i'al refrigeratingcircuit in which said compressor withdraws low pressure refrigerant fromsaidnaccumulator and through said casing and discharges high pressurerefri'ger'ant to said condenser, said motor being cooled by the lowpressure refrigerant in said casing, means for periodically warming saidevaporator to defrosting temper'atures by means of hot compressedrefrigerant comprising an auxiliary circuit having aninle't endconnected to said normal refrigerating circuit between said compressorand said condenser and it's outlet end connected to said normalrefrigerating circuit "between the outlet end of said evaporator andsaid compressor, said auxiliary circuit including a defrost portion inheat exchange relation with said evaporator and a flow restrictingmeans, conduit means connecting said compressor, said defrost portion,said flow restricting means and said casing to form a series-flowdefrosting circuit, a normally closed valvein said auxiliary circuit forcontrolling flow of refrigerant through said circuit, said flowrestricting means in said auxiliary circuit having a flow restrictionsuflicient to maintain condensing pressures in said .defrost sectionwhen refrigerant is flowing through said defrost section butsubstantially less than the flow restriction providedby said fixed flowrestrictor when said valve is opened whereby opening of said valvecauses substantially all of the circulating refrigerant to flow throughsaid defrost circuit, said defrost bircuit'having a lower effectivevolume than said normal refrigerant circuit'whereby the amount ofrefrigerant in said casing and therefor the load on said motor 'arehigher during defrosting operation of said system than during .normalrefrigerating operation thereof, aportion of .said auxiliary circuitbetween said valve and-said defrost portion being in heat vexchangerelation with said refrigerating circuit between said \condenser andsaid capillary flow restrictor to vaporize any refrigerant flowing tosaid capillary flow restrictor and thereby limit flow of refrigerant tosaid evaporator during operation of said system when said valve is inthe open position.

References Cited in the file of this patent UNITED STATES PATENTS1,863,427 Warren June 14, 1932 2,080,358 Kucher May 11, 1937 2,693,683Toothman :Nov. 9, 1954 2,720,759 Philipp Oct. 18, 1955 2,759,339 KundertAug. 21, 1956

